As a fueling portion structure for fueling a fuel tank of an automobile or the like, there is a structure in which the fueling port, into which a fueling nozzle is inserted, can be opened and closed by an opening/closing valve such as a flapper valve or the like. For example, in Japanese Patent Application Laid-Open No. 8-142694 (Patent Document 1), there is disclosed a structure provided with a valve body that is supported so as to rotate freely at the fuel flow-in port. This valve body is urged in the valve-closing direction by a spring. Further, due to a fueling gun being inserted into the fueling port, the valve body is rotated in the opening direction against the urging force of the spring.
However, in the structure of the aforementioned publication, the urging force of the spring becomes greater as the valve body rotates in the opening direction. In particular, the valve body, that has moved to the open-valve position, presses against the fueling gun with a large urging force. Therefore, the resistance when the fueling gun is pulled out is large.
Among fueling guns, there are those that are structured to have a local large-diameter portion, due to a coil spring being wound on the outer periphery of the distal end portion, or the like. With such a fueling gun, there are cases in which the large-diameter portion strongly catches on the housing of the fueling port (the fueling port member), and pulling-out becomes more difficult.